The need to convey a product is frequently encountered during many industrial processes. For example, an extruder is a well known apparatus utilized to provide continuous mixing and conveyance of ingredients of a product. Extruders are widely used in many industries, e.g. the chemical and food processing industries, to continuously mix ingredients of a product and to form the product by conveying the mixed ingredients through a die having a preselected shape. The continuous processing provided by an extruder often results in an efficient and cost effective alternative to batch processing techniques.
Extruders typically include an arrangement of inlet ports for ingress of various ingredients to be mixed by the extruder, into a mixing chamber. The mixed ingredients are forced through the extrusion die by the conveying action of various mechanical elements and onto a conveyor or other processing mechanism for cutting and further processing. The cross-section of the extrusion die is arranged to form the mixed ingredients (referred to as the extrudate), as it is forced through the die, into a desired shape for the product.
Conveyance of a mixture of ingredients through a die often occurs under laminar flow conditions. Product flow under these conditions causes maximum flow velocity at the center of flow, with those portions of the product in contact with surfaces, such as, e.g., extruder die surfaces, tending to adhere to the surfaces due to the friction. In such circumstances, it is typical for the surfaces of the mixed ingredients in contact with the surfaces of the extruder die to encounter friction due to the relative movement of the product over the extruder surfaces. This results in shear forces throughout the product as it is conveyed through the extruder and forced through the extrusion die.
The presence of laminar flow with shear forces can degrade product quality. This is particularly true in shear sensitive products, i.e., products that are susceptible to degradation due to the shear forces. Thus, the advantages of continuous mixing and conveying afforded by extrusion processing can be overcome by product degradation when applied to a shear sensitive product, particularly when the shear sensitive product is of a relatively high viscosity. Moreover, the shear forces can cause physical break up of the product as it is forced through an extrusion die, resulting in degradation of the internal structure and integrity of the product.
In certain ingredient mixing operations, desired chemical reactions occur between the ingredients. Often the chemical reactions affect the rheological properties of the product. For example, a setting solution can be mixed with other liquid ingredients to set the ingredients into a solid or gel state for shaping and forming. Setting reactions are also utilized to reconstitute food products so that solutions, e.g., containing a source ingredient, can be reconstituted into a gel having the texture and consistency of the original food product used to provide the source ingredient.
A problem with utilizing a continuous extrusion process to obtain a set extrudate is that when the product begins to set within the extruder, the possibility of degradation and physical break up of the extrudate during conveyance increases after the transition of the mixed ingredients from a liquid phase to a highly viscous solid or gel phase. The high viscosity of the setting gel increases shear forces throughout the extrudate as it is conveyed through the extruder. When the final mixture of the product is shear sensitive, the extrudate tends to degrade and break apart, at least sporadically, as it is conveyed through the extrusion die, significantly limiting the ability to continuously convey, shape, form and cut the extrudate in an efficient and continuous manner.
Thus, the desirability and efficiency of continuously processing and conveying ingredients undergoing a simultaneous chemical setting reaction becomes problematical, particularly in an extrusion process. The inherent continuous mixing, conveying, forming and shaping aspects of an extrusion operation are rendered ineffective for shear sensitive products, especially those undergoing setting reactions, due to a continuously increasing viscosity and resultant generation of damaging shear forces, as the mixed ingredients transition during conveyance through the extruder, from a liquid phase to a solid phase. Heretofore known systems do not provide a method of product conveyance suitable to reduce shear forces so that, e.g., an extrusion process of the type described above, can be effectively performed.